1 /*
2 * ALSA timer back-end using hrtimer
3 * Copyright (C) 2008 Takashi Iwai
4 *
5 * This program is free software; you can redistribute it and/or modify
6 * it under the terms of the GNU General Public License as published by
7 * the Free Software Foundation; either version 2 of the License, or
8 * (at your option) any later version.
9 *
10 * This program is distributed in the hope that it will be useful,
11 * but WITHOUT ANY WARRANTY; without even the implied warranty of
12 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
13 * GNU General Public License for more details.
14 *
15 * You should have received a copy of the GNU General Public License
16 * along with this program; if not, write to the Free Software
17 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
18 *
19 */
20
21 #include <linux/init.h>
22 #include <linux/slab.h>
23 #include <linux/module.h>
24 #include <linux/moduleparam.h>
25 #include <linux/hrtimer.h>
26 #include <sound/core.h>
27 #include <sound/timer.h>
28
29 MODULE_AUTHOR("Takashi Iwai <tiwai@suse.de>");
30 MODULE_DESCRIPTION("ALSA hrtimer backend");
31 MODULE_LICENSE("GPL");
32
33 MODULE_ALIAS("snd-timer-" __stringify(SNDRV_TIMER_GLOBAL_HRTIMER));
34
35 #define NANO_SEC 1000000000UL /* 10^9 in sec */
36 static unsigned int resolution;
37
38 struct snd_hrtimer {
39 struct snd_timer *timer;
40 struct hrtimer hrt;
41 bool in_callback;
42 };
43
snd_hrtimer_callback(struct hrtimer * hrt)44 static enum hrtimer_restart snd_hrtimer_callback(struct hrtimer *hrt)
45 {
46 struct snd_hrtimer *stime = container_of(hrt, struct snd_hrtimer, hrt);
47 struct snd_timer *t = stime->timer;
48 ktime_t delta;
49 unsigned long ticks;
50 enum hrtimer_restart ret = HRTIMER_NORESTART;
51
52 spin_lock(&t->lock);
53 if (!t->running)
54 goto out; /* fast path */
55 stime->in_callback = true;
56 ticks = t->sticks;
57 spin_unlock(&t->lock);
58
59 /* calculate the drift */
60 delta = ktime_sub(hrt->base->get_time(), hrtimer_get_expires(hrt));
61 if (delta.tv64 > 0)
62 ticks += ktime_divns(delta, ticks * resolution);
63
64 snd_timer_interrupt(stime->timer, ticks);
65
66 spin_lock(&t->lock);
67 if (t->running) {
68 hrtimer_add_expires_ns(hrt, t->sticks * resolution);
69 ret = HRTIMER_RESTART;
70 }
71
72 stime->in_callback = false;
73 out:
74 spin_unlock(&t->lock);
75 return ret;
76 }
77
snd_hrtimer_open(struct snd_timer * t)78 static int snd_hrtimer_open(struct snd_timer *t)
79 {
80 struct snd_hrtimer *stime;
81
82 stime = kzalloc(sizeof(*stime), GFP_KERNEL);
83 if (!stime)
84 return -ENOMEM;
85 hrtimer_init(&stime->hrt, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
86 stime->timer = t;
87 stime->hrt.function = snd_hrtimer_callback;
88 t->private_data = stime;
89 return 0;
90 }
91
snd_hrtimer_close(struct snd_timer * t)92 static int snd_hrtimer_close(struct snd_timer *t)
93 {
94 struct snd_hrtimer *stime = t->private_data;
95
96 if (stime) {
97 spin_lock_irq(&t->lock);
98 t->running = 0; /* just to be sure */
99 stime->in_callback = 1; /* skip start/stop */
100 spin_unlock_irq(&t->lock);
101
102 hrtimer_cancel(&stime->hrt);
103 kfree(stime);
104 t->private_data = NULL;
105 }
106 return 0;
107 }
108
snd_hrtimer_start(struct snd_timer * t)109 static int snd_hrtimer_start(struct snd_timer *t)
110 {
111 struct snd_hrtimer *stime = t->private_data;
112
113 if (stime->in_callback)
114 return 0;
115 hrtimer_start(&stime->hrt, ns_to_ktime(t->sticks * resolution),
116 HRTIMER_MODE_REL);
117 return 0;
118 }
119
snd_hrtimer_stop(struct snd_timer * t)120 static int snd_hrtimer_stop(struct snd_timer *t)
121 {
122 struct snd_hrtimer *stime = t->private_data;
123
124 if (stime->in_callback)
125 return 0;
126 hrtimer_try_to_cancel(&stime->hrt);
127 return 0;
128 }
129
130 static struct snd_timer_hardware hrtimer_hw = {
131 .flags = SNDRV_TIMER_HW_AUTO | SNDRV_TIMER_HW_TASKLET,
132 .open = snd_hrtimer_open,
133 .close = snd_hrtimer_close,
134 .start = snd_hrtimer_start,
135 .stop = snd_hrtimer_stop,
136 };
137
138 /*
139 * entry functions
140 */
141
142 static struct snd_timer *mytimer;
143
snd_hrtimer_init(void)144 static int __init snd_hrtimer_init(void)
145 {
146 struct snd_timer *timer;
147 int err;
148
149 resolution = hrtimer_resolution;
150
151 /* Create a new timer and set up the fields */
152 err = snd_timer_global_new("hrtimer", SNDRV_TIMER_GLOBAL_HRTIMER,
153 &timer);
154 if (err < 0)
155 return err;
156
157 timer->module = THIS_MODULE;
158 strcpy(timer->name, "HR timer");
159 timer->hw = hrtimer_hw;
160 timer->hw.resolution = resolution;
161 timer->hw.ticks = NANO_SEC / resolution;
162
163 err = snd_timer_global_register(timer);
164 if (err < 0) {
165 snd_timer_global_free(timer);
166 return err;
167 }
168 mytimer = timer; /* remember this */
169
170 return 0;
171 }
172
snd_hrtimer_exit(void)173 static void __exit snd_hrtimer_exit(void)
174 {
175 if (mytimer) {
176 snd_timer_global_free(mytimer);
177 mytimer = NULL;
178 }
179 }
180
181 module_init(snd_hrtimer_init);
182 module_exit(snd_hrtimer_exit);
183